[Purpose] The six-minute walk test (6MWT) is increasingly being used as an important tool for analyzing functional capacity in patients with multisystem disorders. The aim of this study was to evaluate the effect of body composition, peripheral muscle function, and pulmonary function on the six-minute walk distance (6MWD) in acromegalic patients. [Subjects and Methods] Thirty-two patients with active acromegaly, with a mean age of 48.6 ± 12.1 years, underwent an evaluation of body composition using electrical bioimpedance, isometric dynamometry with surface electromyography, tests of pulmonary function, and the 6MWT. [Results] The mean ± SD values for the 6MWD, fat-free mass (FFM), and maximal expiratory pressure (MEP) were 65.5 ± 11.7% predicted, 55.1 ± 10.6 kg, and 55.2 ± 16.8% predicted, respectively. There was a significant correlation between the 6MWD and the following parameters: the angle of the linear regression line obtained using the values of the median frequency electromyography signal over time during the fatigability test for the vastus medialis muscle (MDF, r=0.65), FFM (r=0.62), MEP (r=0.60), height⁽²⁾/resistance index (r=0.52), resistance (r=−0.50), and forced expiratory volume in 1 second (r=0.50). Multivariate analysis showed that MDF, FFM, and MEP were independent predictors of the 6MWD (R²=0.52). [Conclusion] The fatigability of the peripheral muscles, FFM, and MEP are the primary determinants of the 6MWD in acromegalics.